Polymerization of conjugated diene hydrocarbons



Patented July 31, 1945 U ITED STATES POLmBIZATION- OF OONJUGATED DIENE HYDROCABBONS George L. Browning, Jr., William D. Stewart, and

Benjamin M. G. Zwicker, Akron, Ohio, assignors, by meme assignments, to. The B. F. Goodrich Company, Akron, Ohio, a corporation New York No Drawing. Application May 81, 1941, Serial No. 396,158

10 Claims.

This invention relatesto the polymerization of butadiene hydrocarbons, and particularly to a method whereby butadiene hydrocarbons may be polymerized in an aqueous emulsion to form products closely resembling natural crude rubber.

It is disclosed in the oopending application of Charles F. Fryling, Serial No. 396,155, filed May 31, i941, that compounds containing a 2-thiothiazyl group modifyv the emulsion polymerization oi butadiene hydrocmbons in such a manner that polymers more nearly resembling natural rubber are produced. We have discovered that although polymers exhibiting desirable properties are produced in the presence of compounds containing a 2-thiothiazylgroup, the polymerizations are ordinarily somewhat slower when a 2-thiothiazyl compound is included in the recipe. 1

We have found that ii a small amount, ordinarily less than .l% based on the monomers, of a simple ionizable cobalt salt is included in the emulsion during the polymerization, the inhibiting eiiect of the modifiers is counteracted and the activity of the modifiers is increased.

Any modifier containing the 2-thiothiazy1 group which may be represented. by the following structural formula:

captothiazoles include the aromatic thiazoles, by which is meant compounds in which the carbon atoms numbered 4 and 5 form part oi an unsaturated carbocyclic ring, such as Z-mercaptobenzothiazole, Z-mercaptonaphthothiazole, and the corresponding aromatic bis-thiazyl-B mono-, (11-, and polysulfides. 2-thiazyl sulfides such as 4,5-dimethylthiazyl-2 diethylamino sulfide, ben-- zothiazyl-z dicyclohexylamino sulfide, and other compounds containing the 2-thiazyl group'may also be employed. The compounds in which the basicity is in reased by the presence of nitrogenous substituents, for instance, exhibit .activlty as modifiers, but theyuilso retard the polymerization. The use oi appropriate amounts 0!.

the cobalt salts herein described counteracts this effect and allows the polymerizations to conpossess as great activity as the aliphatic z-merducted in reasonable lengths of time.

The proportion in which the z-thiothiazyl compound is included in the composition depends somewhat upon the properties desired in the product, the higher proportions of modifier in general producing softer, more soluble polymers. Very small amounts of modifier such as 0.l%-or even less based on the monomers in the emulsion may profoundly afiect the nature of the polymer produced, and amounts up to 5% or over may advantageously be employed.

By the term simple ionizable cobalt salt" is meant the simple inorganic or organic cobalt salts which yield ions in aqueous solution. The salt need not be completely or even moderately soluble in water in order to be employed since even relatively insoluble salts are known to ionize to a limited extent. The term simple ionizable sal distinguishes from complex compounds in which the cobalt is united to other elements in the compound by coordinated covalences and is meant to include only those compounds in which the metal exerts its primary positive valences.

Among the simple ionizable cobalt salts which may be employed may be mentioned the chlorides, bromides, nitrates, sulfates, carbonates, borates, acetates, sulfites, thiosuliates, oyanldes, and sulfides, the water-soluble salts including the halides, sulfates, and nitrates being preferred. Cobaltous or cobaltic salts, or a mixture of the oxidized and reduced forms may be used. It is generally desirable to employ the cobalt salt in amounts not greater than .l% based on the monomers, although this is not a critical value, and amounts as great as 1% and more may be used in some instances, some systems exhibiting a. greater tolerance towards excess cobalt salt than others. The use of too reat amounts of cobalt salt will increase the time required for the polymerization to reach completion.

As a specific example of the use of the cobalt salts, a mixture of parts by weight of hutadiene and 45 parts of acrylonitrile was copolymerized at 30 C. in the presence of about 250 parts of a 3% aqueous solution of myristic acid which had been neutralized with sodium hydroxide, 0.35 part of hydrogen peroxide as an initiator, 0.05 part of cobaltous chloride, and 0.5 part of 2-mcrcaptobenzothiazole. The poLvmerization required 19 hours and the polymer obtained by coagulating the latex-like product oi. the polymerization attained a maximum tensile strength 01.4900 lbs/in. and a maximum ultimate elongation of 440% when tested in a tire tread recipe. When the experiment was repeated with omission of the cobaltous chloride, the polymerization required 28 hours, and the polymer attained a maximum tensile strength or only 3800 lbs/in. and an elongation at only 800%, while repetition of the experiment with the omission of the z-mercaptobenzothiazole required 19 hours, and yielded a polymer exhibiting. a maximum tensile strength of 3950 lbs/in. and an elongation of 280% when tested in the same treacl recipe. It can be seen that the combination of a ii-thiothiazyl compound and a cobalt salt produced a polymer superior to those obtained in the absence of either the 2-thiothiazyl like products were coagulated and washed, and

age resulting products were tested for solubility in benzene, and were vulcanized in a tire tread.

Hie presence of the cobalt in the above poly merizstion not only shortened the time necessary for the experiment to reach completion, but the products had a greater resemblance to natural rubber in respect to solubility of the to than those prepared in the am sense or either the cobalt or the Z-thiotl warn;

e modifying agents of this invention may be,

employed in the poerizationin aqueous emul= sion oi butediene hydrocarbons such as hu todiene, 2,3-elhuteoiene, isoprene, or pl meryiehe either alone or in admixture with each other or with other monomers copolymeriesble therewith. As examples oi monomers copolymerisable with buene hydrocsrhons may is mentioned such compounds es styrene, in-3' nophne, scrylonitrlle, -thsmylonitril me 1: methocrylete, vinyl iidcne ode, methyl vinyl lsetone, methyl vinyl ether,

recipe. The following results were obed:

Amount, 3 g? Tensile Modifier by benzene st l: Elong.

weight Weent inlbs. in.

z-pto-d-eth lthiasolo. 0. it 17.5 I 4.0% 600 Di-2- sl ethyl) t iazyl dl- I s o .40 34.0 3, 000 650 z-meros tol,0-dimethyls .49 18.6 4,01%) 580 Didi-(+6 dimethyl) thlcsyl dis-dill .40 42.0 3,900 020 e-mermpto-emethyl-o-cnrbetho hiazola .68 10.5 3,900 800 Q-mercapto--phenyi thicso .2 .65 20.0 4, 200 670 Di-E-i-phimyl) thiasyl (ii-- do .65 31.0 3,750 020 fi-msrceptobenscthinsole. 56 12. 0 4, 200 420 fi-msreo pto-t-nitm thiaco o 12.0 5,650 720 I assume Any of the ordinary emulsifying agents such as iatty acid soaps including sodium oleatc and The terms "butadiene hydrocarbons and a butadiene hydrocarbon" signiiy butadiene-lfi and its homologues which enter into polymerisation reactions in substantially the same manner. The term sulflde" is a generic term including the mono-. di-. and polysulildes.

Although we have herein disclosed specific embodiments of our invention, we do not intend to limit the invention solely thereto, lot it will be obvioustothoseskilledintheartthatmany vtions and modifications are within the spirit and scope or the invention as defined in the appended claims.

We claim:

1. The method which comprises polymer a conjugated butadiene hydrocarbon in the form of an aqueous emulsion in the presence 01 a compound containing the Z-thiothiazyl group and a.-

simple ionizable cobalt salt.

2. The method which comprises polymerizing a conjugated butadiene hydrocarbon in the form oi an aqueous emulsion in the presence or as smercaptothiazole and a water-soluble cobalt salt.

3. The method which comprises copo 1...: ing in the form 0! an aqueous emulsion butadiene and a smaller amount or a monomer copolymerizable therewith in aqueous emulsion m the presence of a. 2-mercaptothiazole and less than 0.1% based onthe materials polymerized oil a water-soluble cobalt salt.

4, The method which comprises copolymerising butadiene and acrylonitrile in the torso oi an aqueous emulsion in the presence of an aliphatic z-mercaptothiazole and less than 0.1% based on the materials polymerized ot a water=sciub1e cobalt salt.

5. The method or claim 4 in which the thinsols materials polymerized of a water-soluble cobalt salt.

8. The method which comprises copolymerilins butadiene and acrylonltrile in the form of en aqueous emulsion in. the presence of an aliphetic bis-thiazyl-Z disulflde and less than 0.1% based on the materials polymerized oi a water-soluble cobalt salt.

0.. The method of claim 8 in which the bis-= thiasyl-z disulfide is bis-l,5-d.imethylthiewl-2 10. The method which comprises no a conjugated butadiene hydrocarbon in the form of an aqueous emulsion in the presence oi scampound containing the z-thiothiazyl group and less than 0.1% based on the material poized of cobaltous chloride.

GEORGE L. BROWNING, JR. WIILIAM D. STEWART. BENJ M. G. Z 

